Optical correlators and other optical processors using holographic elements to effect geometric transforms have been known for over twenty years. The earliest devices used film for input and output and, hence, did not operate in realtime. However, recent advances in spatial light modulator technology now allow images to be input to optical processors at video frame rates.
An optical correlator uses the Fourier transform property of lenses to convolve an input image with a target image to produce an output image. If the target image appears at a given position in the input image, then the output image contains a peak at that position. A Hough transform processor operates in an analogous manner to produce a peak corresponding to the occurrence of lines in the input image. Current practice is to detect and read out the output image using a CCD or CID detector array, digitize the values of each pixel, and then search the image in a serial manner using a computer. However, it is well known that electronic computers have difficulty interpreting images at video rates. The electronic computer thus becomes a processing bottleneck, reducing the overall data processing rate of the system. There is therefore a need for a technique for accelerating the speed of the electronic processing components of optical correlators.